bc

- arbitrary precision arithmetic language

Synopsis

/usr/bin/bc [-c] [-l] [file]...

/usr/xpg6/bin/bc [-c] [-l] [file]...

Description

The bc utility implements an arbitrary precision calculator. It takes input from any files given, then reads from the standard input. If the standard input and standard output to bc are attached to a terminal, the invocation of bc is interactive, causing behavioral constraints described in the following sections. bc processes a language that resembles C and is a preprocessor for the desk calculator program dc, which it invokes automatically unless the -c option is specified. In this case the dc input is sent to the standard output instead.

Usage

The syntax for bc programs is as follows:

L

Means a letter a-z,

E

Means an expression: a (mathematical or logical) value, an operand that takes a value, or a combination of operands and operators that evaluates to a value,

S

Means a statement.

Comments

Enclosed in /* and */.

Names (Operands)

Other Operands

Arbitrarily long numbers with optional sign and decimal point. Strings of fewer than BC_STRING_MAX characters, between double quotes ("). ( E )

sqrt ( E )

Square root

length ( E )

Number of significant decimal digits.

scale ( E )

Number of digits right of decimal point.

L ( E , ... , E )

Operators

+ - * / % ^

(% is remainder; ^ is power)

++ --

(prefix and postfix; apply to names)

== <= >= != < >

= =+ =- =* =/ =% =^

Statements

.string

Function Definitions

Functions in -l Math Library

s(x)

sine

c(x)

cosine

e(x)

exponential

l(x)

log

a(x)

arctangent

j(n,x)

Bessel function

All function arguments are passed by value.

The value of a statement that is an expression is printed unless the main operator is an assignment. Either semicolons or new-lines may separate statements. Assignment to scale influences the number of digits to be retained on arithmetic operations in the manner of dc. Assignments to ibase or obase set the input and output number radix respectively.

The same letter may be used as an array, a function, and a simple variable simultaneously. All variables are global to the program. auto variables are stacked during function calls. When using arrays as function arguments or defining them as automatic variables, empty square brackets must follow the array name.

Options

The following operands are supported:

-c

Compiles only. The output is dc commands that are sent to the standard output.

/usr/bin/bc

-l

Defines the math functions and initializes scale to 20, instead of the default zero.

/usr/xpg6/bin/bc

-l

Defines the math functions and initializes scale to 20, instead of the default zero. All math results have the scale of 20.

Operands

The following operands are supported:

file

A pathname of a text file containing bc program statements. After all cases of file have been read, bc reads the standard input.

Examples

Example 1 Setting the precision of a variable

In the shell, the following assigns an approximation of the first ten digits of n to the variable x:

x=$(printf "%s\n" 'scale = 10; 104348/33215' | bc)

Example 2 Defining a computing function

Defines a function to compute an approximate value of the exponential function:

scale = 20
define e(x){
    auto a, b, c, i, s
    a = 1
    b = 1
    s = 1
    for(i=1; 1==1; i++){
        a = a*x
        b = b*i
        c = a/b
        if(c == 0) return(s)
        s = s+c
    }
}

Example 3 Printing the approximate values of the function

Prints approximate values of the exponential function of the first ten integers:

for(i=1; i<=10; i++) e(i)

or

for (i = 1; i <= 10; ++i) {         e(i) }

Environment Variables

See environ(5) for descriptions of the following environment variables that affect the execution of bc: LANG, LC_ALL, LC_CTYPE, LC_MESSAGES, and NLSPATH.

Exit Status

The following exit values are returned:

0

All input files were processed successfully.

unspecified

An error occurred.

Files

/usr/lib/lib.b

mathematical library

/usr/include/limits.h

to define BC_ parameters

Attributes

See attributes(5) for descriptions of the following attributes:

See Also

dc(1), awk(1), attributes(5), environ(5), standards(5)

Notes

The bc command does not recognize the logical operators && and | |.

The for statement must have all three expressions (E's).